Controlling Traffic in a Packet Switched Communications Network

Abstract

The present invention relates to a packet switched communications network especially to an Ethernet network in which User Network Interfaces (UNI) are standardized between client network ( 202 ) and core network ( 203 ) with a number of UNI service attributes. In one aspect of the invention a method is used in current packet switched nodes implementing a policer function. The task of the function is to decide whether packets with high drop preference need to be dropped or not due to resource shortage on the given interface. All outgoing packets at a given port will undergo this policer ( 401 ) irrespective of the source, destination, identification codes or traffic class. Policer ( 401 ) drops packets with high drop preference in one traffic class before a packet of low drop preference is dropped in any other traffic class, and drops packets with high drop preference before a packet of low drop preference is dropped in the same queue. In the course of dropping packets, policer ( 401 ) prevents the reordering of packets with low drop preference and packets with high drop preference within the same flow.

1 - 12 . (canceled) 
   
   
       13 . A method for controlling traffic in a packet switched communications network comprising network nodes, in which network packets of flows can be distinguished by drop preference and can be put into queues according to traffic classes, said method comprising the steps of:
 dropping packets with high drop preference in one traffic class before a packet of low drop preference is dropped in any other traffic class;   dropping packets with high drop preference before a packet of low drop preference is dropped in the same queue; and   preventing reordering of packets with low drop preference and packets with high drop preference within the same flow.   
   
   
       14 . The method of  claim 13 , wherein the packets are dropped with high drop preference in one traffic class before packets with low drop preference are dropped in any other traffic class, except for Best Effort (BE) packets. 
   
   
       15 . The method of  claim 13 , wherein the steps of dropping packets are controlled by a token bucket having a token rate which is indicative of link rate on an outgoing interface of the network node. 
   
   
       16 . The method of  claim 15 , further comprising the steps of:
 analyzing each incoming packet by the drop preference;   deciding if the packet is of low drop preference;   forwarding packets with low drop preference onto output queues and consuming a token from the token bucket if available;   forwarding packets with high drop preference onto the output queues if there is an available token in the token bucket, and consuming the token from the token bucket if available; and   dropping packets with high drop preference if there is no available token in the token bucket.   
   
   
       17 . The method of  claim 16 , wherein the method further comprises the steps of:
 deciding whether the packet is a Best Effort (BE) packet;   processing the packet with high drop preference if the packet is a Best Effort (BE) packet; and   processing the packet with low drop preference if the packet is not a Best Effort (BE) packet.   
   
   
       18 . The method of  claim 13 , wherein the packet switched communications network is an Ethernet network in which traffic is forwarded by flow of frames, and the dropping preference is represented by a drop eligible (DE) bit in an Ethernet frame. 
   
   
       19 . A network node in a packet switched communications network capable of distinguishing packets by drop preference, said network node comprising a policer including:
 an analyzer for receiving incoming packets and identifying the drop preference bits in a packet header;   decision logic for deciding whether the packet is to be forwarded or dropped; and   a transmitter receiving packets from the analyzer and transmitting or dropping the packets according to the decision of the decision logic.   
   
   
       20 . The network node of  claim 19 , wherein the policer further includes a token bucket control, wherein token rate is indicative of link rate of an outgoing interface of the network node. 
   
   
       21 . The network node of  claim 20 , wherein the rate of a token bucket is equal to or less than the link rate of the outgoing interface of the network node. 
   
   
       22 . A packet switched communications network comprising network nodes connected to each other, in which network packets can be distinguished by drop preference and can be put to queues according to traffic classes, wherein at least part of the network nodes comprise a policer configured to:
 drop packets with high drop preference in one traffic class before a packet of low drop preference is dropped in any other traffic class;   drop packets with high drop preference before a packet of low drop preference is dropped in the same queue;   prevent the reordering of network packets with low drop preference and packets with high drop preference within a same flow.   
   
   
       23 . The packet switched communication network of  claim 22 , wherein the packet switched communications network is implemented as an Ethernet network, wherein traffic is forwarded by flow of frames, and the dropping preferences are represented by Drop Eligible (DE) bits.